Brian McKay, Topaz Inc., and Elaine

Maruca, PLIDCO®, USA, focus on safe

and reliable methods that facilitate

pipeline repairs/modifications without

system shutdown.

Is it routine maintenance? Is it an emergency? Whatever the reason, operations personnel do not take shutting down a system, for any reason, lightly. Time and product lost in taking a line out of service, making the repair or modification and then bringing the line back up, feels like pouring money down the drain. This is why, if the

project can be completed safely while the line remains in service, that is the option that will be chosen every time. That is when hot tapping and associated procedures become practical and cost-effective solutions.

You have no doubt heard of hot tapping before, whether you utilise the procedure routinely or not. While the overall concept of hot tapping is not overly technical, the actual procedures become a bit complex with the introduction of potentially hazardous products under high pressure and at extreme temperatures. Let us look at a brief overview of the hot tapping procedure and several scenarios where hot tapping can facilitate other maintenance or repair tasks.

The basicsHot tapping, sometimes called pressure tapping, cold tapping or wet tapping, is a field machining process that enables tie-ins to onstream pipe, tanks, or any pressurised gas or liquid containing vessel. This is done without shutting down service and without release or loss of product. Hot tapping also permits the insertion under pressure of sensing or metering devices into the flowstream, installation of permanent or temporary bypass piping, and is the preparatory stage for line plugging (isolation) operations.

A hot tap is accomplished by penetrating the vessel wall within the confines of a tapping or branch connection. This branch connection consists of a tapping fitting welded

or bolted to the vessel to be tapped. The fitting is usually some variant of a self-reinforcing connection with attached flange, a short flanged pipe nipple saddle cut to fit the vessel, or a flanged full encirclement tapping tee. A tapping valve is attached to the tapping fitting as a means to block in line pressure once the hot tap is complete. Bolted to and operating through the open tapping valve, the tapping machine extends a shell cutter to the vessel wall, mills a ‘coupon’ out of the vessel the approximate diameter of the branch ID, then retracts the shell cutter with the coupon back through the tapping valve. The valve is then closed, pressure is bled off the tapping machine and the machine is removed. The tapping valve is now ready to receive the new branch piping. When planning a hot tap, critical information must be provided:

) Size of tapping valve through which hot tap will be done.

) Is the valve threaded or flanged? ANSI rating? (150#, 300#, 600#, etc.)

) Nominal size, wall thickness and material of the line to be tapped.

) Product in the line to be tapped.

) Operating pressure and temperature of the product.

) Overall length of tapping nozzle and valve (distance from the surface being tapped to the outside of the tapping valve).

Once onsite, and prior to beginning a tap, there are details that the hot tap technician must address to assure the safe and trouble-free completion of the hot tap. These details include checking the tapping valve and nozzle flange alignment, proper positioning of gaskets, assuring that flanged connections are properly bolted, assuring that the tapping valve is a full opening/full port valve with sufficient ID for clearance of the cutter being used, and ensuring that no trash, bolts or welding rods have been left or fallen into the tapping valve or nozzle. Accurate measurements are taken and recorded to enable calculation of the point at which the pilot drill and shell cutter will touch the vessel wall and when the cutter will have travelled far enough to complete the cut (Figure 1). Next, the power source is connected to the tapping machine; the machine can be powered pneumatically, hydraulically or by an electric motor. The tapping machine is equipped with an automatic feed mechanism and the technician monitors the calibrated travel indicator continuously during the slow milling process to assure that at no point does either the cutter travel beyond the centreline of the tapping pipe, or that the pilot drill touches the back wall of the pipe. Topaz Inc. in Houston, Texas, specialises in hot tapping service work and they also sell several styles of saddles including PLIDCO Hot Tapping+Saddles that bolt-on. PLIDCO offers options including hinges, plated studs and nuts, anodes, epoxy paint and integral clamp elements (Figure 2).

Tapping into a blind flange or a heavy wall vesselHot tapping thick wall pipe, vessels and blind flanges several inches thick is possible. There are, however, special issues that

Figure 1. Before connecting the power source to the hot tapping machine, the Topaz technician confirms his calculation at which the pilot drill should make contact with the vessel.wall.

Figure 2. A subsea PLIDCO Hot Tapping+Saddle with integral clamping elements, epoxy paint, plated studs and nuts, anodes, lifting eyes and a hinge.

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need to be addressed in the design phase of the tapping branch. This service requires special engineered solutions that address specific challenges on a job-by-job basis. Topaz personnel can work closely with the Engineering department at PLIDCO to design what is needed for each application.

Hot tapping materials other than carbon steelA pipe or other vessel needs to be hot tapped that is not carbon steel. Can it be done? The answer is yes. Cement lined pipe, transite, cast iron, stainless steel and other alloys, plastic and fibreglass can all be tapped. It is critical to know the thickness and composition of the lining, hardness of the alloy, and type of fitting and valve through which the tap will be performed to insure that proper equipment is selected and provided for the job.

Tapping into vessels at an angleNow things start getting a little trickier, but are still feasible. Tapping a radial surface like round pipe is common and presents no special challenge, provided the tapping nozzle is installed perpendicular to the vessel wall. There are times, however, when the new piping layout requires tapping the vessel wall at an angle other than 90˚. Angle taps like this require special tapping equipment and tapping nozzle preparation, so contacting Topaz before welding is important. Topaz has performed angle hot taps up to 24 in. nominal valve size, at an angle of 45° maximum off perpendicular (the centreline of the tapping nozzle actually intersects the centreline of the line being tapped at 45˚, the nozzle is not simply ‘rolled’ 45˚ off a vertical or horizontal orientation). Utilising these same specialised tools and nozzle prep, we can also make hot taps into the heel or backside of short and long radius 90˚ ells. When bolt-on fittings are required, they can be custom designed and manufactured at PLIDCO to accommodate angle taps.

Hot tapping when a weld-on tapping nozzle or tee is not possibleThere are two types of hot tapping saddles; bolt-on and weld-on. Hot tapping can still be performed in most situations where it is not safe to weld in the area, when product and flow conditions within the line make welding unsafe, or when the pipe and tapping nozzle or tee is not a material that can be welded. In such cases, a bolt-on fitting, such as the PLIDCO Hot Tapping+Saddle, can be quickly and easily installed by bolting the two halves of the fitting together using the provided torque specification (Figure 3). As the two halves come together against the pipe wall, the integral girdering of the fitting protects, and secures to prevent displacement of the elastomer seals. PLIDCO engineers can design custom hot tap fittings in special configurations and materials for limitation of temperature due to seals where the standard PLIDCO Hot Tapping+Saddle is not suitable.

Probe installation Can appurtenances such as thermowells, flowmeters and atomisers be installed while the line is in service and under pressure? The answer is, in many cases, yes. Knowing the physical design and dimensions of the device often enables adaptations to be made to standard hot tapping equipment and fittings, and permits positioning of the piece through the tapped hole into

the flow stream. Once it is installed in the set position within a specialised fitting, line pressure is contained and the temporary installation equipment can be removed. This allows unobstructed access for attachment of instrumentation.

Plugging a line temporarily to do work downstreamLine plugging is a method of temporarily isolating and bleeding down a section of a pressurised system, for purposes of alteration or maintenance within the isolated part. This is done without

Figure 3. A 6 in. PLIDCO Hot Tapping+Saddle being installed in Italy.

Figure 4. This bypass system allows the flow of product to be maintained around the isolated section while the work is being done.

REPRINTED FROM MAY 2015 / World Pipelines

shutdown of the entire system and without loss of product. If flow must be maintained despite the isolation, a bypass can be installed around the isolated work section (Figure 4).

Line plugging fittings are also available in either a bolt-on or weld-on style. A special line plugging variant of the PLIDCO Hot Tapping+Saddle with a purpose built flange can be bolted on the line and used in the line plugging process when welding is not possible (Figure 5). Bolt-on plugging fittings include integral clamping areas to prevent axial and torsional movement of the fitting due to the inherent end force generated when the line is plugged and the weight of the temporary tapping and plugging equipment. These specialty fittings allow us to work through temporary valves, which Topaz provides, during the plugging operation. In very abbreviated terms, the procedure begins by mounting the temporary valve on the special line plugging fitting. After a hot tap is made, the line plugging tool is run down through the tapped hole into the set position in the line. The work section is blown down, and the repair or modification

work commences (Figure 6). If that scope of work involves having Topaz cold cut a bad section of pipe out to replace it with new pipe, the PLIDCO Weld+End mechanical coupling is a great product to consider. These fittings are safety welding couplings used to quickly join pipe so that flow can be resumed immediately, keeping downtime to an absolute minimum. When flow has been reestablished, the Weld+End can be backwelded if you choose. Welders and weld procedures should be qualified in accordance with API standard 1104, Welding of Pipelines and Related Facilities, Appendix B, In-Service welding. No special preparation of pipe ends is needed to install the PLIDCO Weld+End. When the repair or modification within the isolated work section is finished, the line plugging tool is retracted, and an o-ring sealed metal plug is secured in the special fitting below the temporary valve. Pressure is then bled off above the plug, the valve is removed, and a blind flange is installed on the fitting to complete the job.

If necessary, line plugging work can also be performed through permanent valves and standard hot tap fittings. When plugging through permanent valves, contact Topaz for required bore diameters and overall fitting and valve dimensions prior to welding. Information we require for line plugging services includes:

) Nominal size of the line.

) Will the line be plugged on one end or both ends of isolated section?

) Material and wall thickness (schedule) of the line.

) Product in the line.

) Operating pressure and temperature.

Figure 6. Performing a cold cut in hazardous conditions is a safe and effective technique used when torch cutting is not an option.

Figure 7. PLIDCO Shear+Plug being installed on a 16 in. line containing 100% H

2S.

Figure 5. This PLIDCO Hot Tapping+Saddle with a purpose built flange is being pressure tested to confirm a 100% seal.

World Pipelines / REPRINTED FROM MAY 2015

) Maximum possible pressure and temperature while line is plugged.

) Blow-down and equalisation provisions for de-pressuring and re-pressuring of work section.

) Size of bypass, if required.

) Scope of alteration or maintenance while line is plugged.

) Orientation of the line and required fitting orientation.

Plug a line permanently You can use the same procedure above to plug a line permanently, using bolt-on fittings when desired, with one small addition. You would install a PLIDCO Flange+Coupling with a blind flange to create a seal on the line after the cold cut has been performed. It is common practice to back weld the fitting in place if the

scope of work involves pipeline abandonment or a reroute. This procedure is common onshore as well as offshore. No matter what the situation, PLIDCO will have a safe and reliable solution.

Facing extreme pressure and temperatureHigh pressure, high temperature lines often require a plant shutdown because standard line plugging seals will not safely withstand the extreme pressures and temperatures. A reliable alternative is the PLIDCO Shear+Plug, which provides a safe and reliable way to isolate the problem while keeping the system running. The Shear+Plug provides positive metal-to-metal contact with back up injected sealant. When conventional line plugging techniques cannot stand up to extreme conditions, look to the PLIDCO Shear+Plug alternative for 100% isolation (Figure 7).

REPRINTED FROM MAY 2015 / World Pipelines